Art of dyeing synthetic polymeric



S.., and Victor L.

The present invention relates to the art of dyeing synthetic polymeric materials having parafiinic chains as nuclei and more particularly to a process of dyeing materials made of alpha-olefin polymers and to the product made by this process.

Polymers of alpha-olefins comprise polyethylene, polypropylene and higher polymers of alpha-olefins as described in a paper by Victor L. Erlich entitled Polyolefin Fibers and Polymer Structure, published in the September issue 1959 of the Textile Research Journal. Polypropylene in its so-called isot-actic form, i.e. when all the side chains branching out from the steric configuration of the polymer is such that the linear paraffinic backbone or nucleus of the polymer are all located on the same side of the parafiinic chain is becoming an especially promising material for the commercial production of textile fibers because of its unusual properties, including a comparatively high melting point reaching 176 C. Other higher isotatic poly-alpha-olefins having more than 2 carbons in the straight chain and at least one methyl group in the side chain and having softening points higher than 150 C., are also promising materials for commercial production of textile fibers. We mention as examples isotactic poly-4-methyl pentene-l with a melting point of approximately 240 C. or isotactic poly- 3-methyl butene-l with melting points of between 245 and 300 C.

It is desirable that the poly-alpha-olefin fibers and fiber materials for textile purposes be dyed by the use of dyeing methods, which can be carried out with equipment now commercially available in textile finishing plants and dye works. rials produced from these alpha-olefin polymers, although perhaps accepting dyestuif of various types by means of conventional textile procedures, do not produce a color which is fast to light, i.e. resist fading action when subjected to fadeometer tests for periods of more than 20 hours, or fast to repeated soap washing and repeated dry cleaning. The reason for this deficiency in the dye produced on these fibers by known procedures is the inertness of these polymers to chemical action, the difiiculty of producing a bond between the fiber molecule and the dyestuff and the nearly complete water repellency of the fibers.

One object of the present invention is to provide a new and improved process of dyeing a synthetic polymeric material having a paraffinic chain as a nucleus, and more particularly a poly-alpha-olefin material especially in the fibers, film or similar slender or thin form, which process in the case of fibers permits the use of textile dyeing equipment similar to that now commercially available, and which assures the production on the material of a dye color fast to light, to repeated soap washing and to repeated dry cleaning.

Another object of the invention is to produce a new and improved dyed synthetic material made by the new and improved process described above.

In accordance with the present invention, there is employed an organic dye, which per se, may be conventional, but which is preselected to meet certain physical requirements. These requirements are as follows:

However, it has been found that fiber mate- 3,052,510 Patented Sept. 4, 1962 ICC (1) The dye itself must be fast to heat, light, soap washing and dry cleaning agents.

(2) The dye, per se, must be stable at temperatures at least up to the point slightly below the softening point of the polymeric material to which the dye is to be applied and desirably up to 200 C.

(3) The dye must be water insoluble or at least at the time of application must be in water insoluble form.

(4) The dyestufi as such, this means without requiring the use of an assistant agent, a carrier or a binder, should be insoluble at temperatures up to 60 C. in a parafiin which is liquid at room temperatures (20 C.) or in melted paraffin wax having a melting point of 50 -60 C., and must become soluble in the parafiin or in the melted parafiin wax at least at a temperature slightly below the softening point of the polymeric material which is to be dyed. It has been found desirable in accordance with the present invention to employ a dye which is soluble in the paraffin or in the melted paraffin wax at a temperautre above C. For the purpose of the present invention, the dye is considered to be insoluble in the paraffin or in the melted paraflin wax when the paraffin or the paratfin wax does not take up color from the dye as determined by visible observations with the naked eye and is considered to be soluble in the parafiin or the melted paraffin wax when the paraffin or the melted paraffin wax becomes pronouncedly colored by the dye as determined by visible observation. Thedyes may show similar solubility characteristics in other organic solvents, but insolubility at certain temperatures and solubility at higher temperatures in the paraflin or in the melted parafiin wax have been selected as a yardstick because'the polymers contemplated and especially the alpha-olefin particularly adaptable in the process of the present invention are for instance those commercially designed as vat dyestuffs, but such vat dyestuffs are useful for the purpose of the present invention only when they meet the physical requirements indicated above and when employed in the manner described herein. Dyes which are now commercially used as vat dyes and which have 'been found particularly elfective for the purpose of the present invention, although not used as vat dyes, are those of the indigoid type and especially those indigoid dyes of the halogenated type. Also, indigoid dyes of the thio type can be used.

An example of a halogenated dye of the indigoid type which can be used is: Tetrabromo indigo (Vat Blue 2B).

Examples of thio indigoid dyes which may also be used are as follows:

5',5-dichloro 6,6'-dimethyl 2,2-bisf-thionaphthene indigo (Red 2B) 6,6-diethoxy 2,2'-bis-thionaphthene indigo (Orange R) 2,2-bis-thionaphthene indigo (Pink B) Beta naphthal thio indigoid derivative (Ciba Brown G) of entirely different molecular configuration and composition may be employed as long as they meet the above physical requirements.

The dye selected as described is then applied in accordance with the principles of the present invention. The steps followed in accordance with this process are as follows:

1) The selected dye having the physical characteristics described and in water insoluble form may be dispersed in water to form an aqueous dispersion, and this aqueous dye dispersion with the dye still in'insoluble form is applied to the polymeric material and especially the poly-alpha-olefin in fiber, yarn, fabric, film or other thin or slender form to cause thorough uniform impregnation of the polymer therewith on the surface thereof. It may be desirable to include a wetting agent and an inactive thickening agent in the dye dispersion, such as sodium alginate, but this is not necessary.

Other methods of applying dyestuffs in their finely dispersed water insoluble form may be used provided such operations are carried out in a way to insure intimate contact of the dyestuff with the surface of the material and uniform distribution of such dyestufi over the surface whereby in some instances diffusion of the dyestuff into the core of the polymer occurs.

(2) The polymeric material dye-impregnated on the surface as described is dried to remove substantially all of the water and any volatile solvents or compounds that might be present with the dye. This is accomplished at elevated temperature around or below 100 C.

(3) The dried polymeric material impregnated with dyes as described, is then heated to a temperature between the point at which the dye becomes soluble in the paraffin or melted paraffin wax and the point slightly below the softening point of the polymer, as for example, ap proximately C. below this softening point, but in any case the material is not heated to a temperature at which the dye becomes unstable. This temperature desirably ranges between 110 and 150 C., especially for isotactic polypropylene, and is applied for a period sufficient to cause complete diffusion and firm absorption of the dye by the material. It has been found that this temperature of 110 to 150 C. applied for a period of between 3 to 10 minutes on textile fibers and materials of similar slenderness or thinness is sufiicient to effect uniform diffusion and absorption of the dry dye through the full depth of the material. Polyolefins of higher melting point than that of isotactic polypropylene can withstand higher temperatures and such temperatures could be effectively used as long as they are below the point at which the dye becomes unstable and the material becomes softened. The higher the temperatures used, the deeper and richer is' the color developed in the polymeric material. Because of the absence of water and of other volatile compounds, pressure is not needed during this heat treatment.

(4) The polymer material treated as described in steps 1, 2 and 3 is then thoroughly washed with soap or washed with detergent to remove the unfixed color. This washing is desirably carried out at an elevated temperature but below 100 C.

It has been found surprisingly that polymeric materials of the class described and especially poly-alphaolefins when treated according to steps 2 and 3 described, will cause the dry dye impregiating the surface after step 1 to diffuse uniformly and thoroughly into the very core of the material. Simultaneously, the diffused dye compound becomes firmly absorbed by the polymer. This absorption as indicated by the dee-pness of the color shade becomes more pronounced the higher the temperature. The dyed fabric will then manifest color fastness to light, repeated washings with soap or detergents and repeated dry cleaning and the dye will be otherwise stable.

The bond in the polymer-dye system of the present invention becomes-extremely strong. This strong bond may be due to the solubilization or fusion of the dyestuff into the polymer, to the presence of Van der Waals forces or perhaps to the creation of cross-linking bonds.

As far as certain aspects of the invention are concerned, the polymeric material dyed by the process of the present invention may take any physical form. However, as far as the more specific and more desirable aspects of the invention are concerned, the polymeric material is in thin form to assure the absorption of the dye through the full thickness of the material by thet process of the present invention. For that purpose, the polymeric material would be in the form of a textile fiber, fabric, sheet or film. However, as far as certain aspects of the invention are concerned, the process of the present invention may be applied to thicker materials where it is not necessary to dye the materials throughout their full depth.

Moreover, where the polymer material to be dyed is not in the form of a filament or yarn, but is in some other form, and especially in the form of a film or fabric, then as far as certain aspects of the invention are concerned, the dye need not be applied uniformly over the entire surface of the material but may be applied thereto to form a predetermined pattern or design thereon. In that case, the dye may, for example, be sprayed or rolled onto the film or fabric through a stencil, or applied by a roller through a silk screen, or applied without a stencil or screen but by means of a roller having a dye impressing surface configuration corresponding to the pattern or design to be applied, or applied in any other way to form the desired pattern or design on the polymer material. The dye applied in this predetermined pattern or design form is then firmly absorbed and fixed in the polymer material in said form by the process of the present invention described above.

The following examples illustrate certain ways in which the principle of the invention can be applied but are not to be construed as limiting the broader aspects of the invention.

Example 1 A 100% spun isotactic polypropylene fabric is dipped in a bath at a temperature of between 55 and 60 C. containing an aqueous dispersion of tetrabromo indigo (Vat Blue 213) with a concentration of 8 oz./gal. and containing in solution 2% sodium alginate as a thickener. The fabric so soaked is then passed between rubber rollers to remove the excess. The fabric is then dried to moisture free condition at a temperature between and C. and more specifically at 93 C. in an oven and then heated to 127 C. for 5 minutes in the absence of pressure, i.e. at substantially atmospheric pressure, followed by a thorough isoaping at 70 C. to remove excess color.

The fabric treated as described was uniformly dyed a medium shade of blue with no appreciable change in hand, feel or performance of the fabric. Fa-stness tests with a fadeometer for 25 hours produced no fading of the color, and for 50 hours slight fading. Three successive washings with soap and with soda ash at 70 C. produced negligible changes, and dry cleaning under conditions in which the polymer was not attacked did not affect the fastness of the color.

Example 2 Skeins of 100% isotactic propylene filament yarn are wetted and dipped in a bath at a temperature of between 60 and 65 C. containing 5,5'-dichloro 6,6 dimethyl 2,2 bio-thio-naphthene indigo (Vat Red 2B) with no other additive. The yarn is allowed to air dry to a substantially moisture free condition followed by heating to C. for 5 minutes at substantially atmospheric pressure. The yarn is thoroughly soaped to remove unfixed color. The color imparted to the yarn by this process was a uniform shade of red and this color showed no appreciable fading when the yarn was exposed to the action of a fadeometer for 50 hours. The colored yarn also manifested good fade resistance to 3 successive 40 minute soap washings at 70 C. Good fastness to dry cleaning was also obtained under conditions which did not attack the polymer.

Example 3 A non-woven matted fabric consisting of 70% in weight of polypropylene staple fibers and 30% in weight of polyethylene fibers, the latter having been used as the bonding agent, was thoroughly impregnated and uniformly saturated by spraying onto both sides of the matting an aqueous dispersion containing 4.5 ounces per gallon of vat Orange GR which is an Imine Naphthylimide, at a temperature of 38 C. Excess dyestuff was removed by centrifuging the matted fabric which subsequently was air dryed at 26 C. to a moisture free condition. At this point, the dyestuff had not penetrated substantially into the material; the color of the fabric was developed by subjecting it to a temperature of 120 C. over a. period of 6 minutes in an air oven. To remove unfixed excess color, the fabric was then thoroughly soaked in warm water in presence of a detergent agent. The matting was found to be dyed uniformly a bright orange color with satisfactory light fastness upon fadeometer exposure, and was found to be resistant to commercial laundering as well as to dry cleaning at room temperature.

It should be noted that in connection with the overall dyeing of fibers in the fabric or unwoven form, the process permits the use of substantially conventional textile fiber dyeing equipment.

While the invention has been described with particular reference to specific embodiments, it is to be understood that it is not to be limited thereto but is to be construed broadly and restricted solely by the scope of the appended claims.

What is claimed is:

1. The process of dyeing an alpha-olefin polymeric material having a paraflinic chain as the nucleus and having a softening point above 100 C. to produce a lightand laundering-fast color shade on said material, which comprises applying to the surface of the material in finely dispersed form an organic dye having the properties of being heat and light stable and without assistant agent of being insoluble in liquid paraflin wax at a tempera-ture up to 60 C. but soluble in said paraffin wax at least at a temperature slightly below the softening point of the polymeric material, sa-id dye being applied in water insoluble form and in the absence of any volatile solvent for said dye at a temperature below the temperature at which said dye would be soluble in liquid paraflin wax, and heating the polymeric material with the dye applied thereto while said dye is in dry form to a temperature ranging between the temperature at which said dye is soluble in liquid paraffin wax and a temperature slightly below the softening point of the polymeric material, to cause the dye in the dry state to be diffused into and firmly absorbed within the interior of the material.

2. The process of dyeing an alpha-olefin polymer material in fiber, film and similar thin form having a softening point below 180 C, to produce a lightand laundering-fast color shade on said material, which comprises applying to the surface of the material in finely dispersed form an organic dye having the properties of being heat and light stable and without assistant agent of being insoluble in liquid paraffin wax at temperature, up to C. but soluble in said liquid paraflin wax at least at a temperature slightly below the softening point of the material, said dye being applied in water insoluble form and in the absence of any volatile solvent for said dye at a temperature below the temperature at which said dye would be soluble in liquid paraffin wax, and heating the polymer material with the dye applied thereto while said dye is in dry form to a temperature ranging between the temperature at which said dye is soluble in liquid parafiin wax and a temperature slightly below the softening point of the polymer material for a period sufficient to cause the dye in the dry state to be diffused into and firmly absorbed substantially throughout the thickness of the material.

3. The process of dyeing ene, as described in claim fibers of isotactic polypropyl- 2, wherein heating is carried out at a temperature range of between 110 and 150 C.

4. The process as described in claim 2. of dyeing fibers of isotactic poly-alpha-olefins having more than 2 carbons in the straight nucleus chain and at least one methyl group in the side chain and having softening points higher than 150 C., said heating step being carried out at a temperature of at least 110 C.

5. The process of dyeing as described in claim 2, wherein the polymer material is in fiber, film and similar thin form, and heating is carried out for a period of 3 to 10 minutes.

6. The process of dyeing an alpha-olefin polymer material in fiber, film and similar thin form having a softening point below 180 C. to produce a lightand laundering-fast color shade on said material, which comprises applying to the surface of the material in finely aqueously dispersed form an organic dye having the properties of being heat and light stable and in its pure form of being insoluble in liquid parafiin wax at temperatures up to 60 C. but soluble in said liquid paraflin wax at a temperature above 110 C., said dye being applied in water insoluble form and in the absence of any volatile solvent for said dye and being applied at a temperature below C. and below the temperature at which said dye would be soluble in liquid paraffin wax, drying the polymer material with the dye applied thereto at a temperature between 90 and C. to substantially moisture free condition, subsequently heating the polymer material in an oven at substantially atmospheric pressure to a temperature ranging between C. but not higher than approximately 10 C. below the softening point of the polymer material, for a period of between 3 and 10 minutes in the absence of pressure above substantially atmospheric pressure and removing the unfixed dye from the surface of the polymer material.

References Cited in the file of this patent UNITED STATES PATENTS 2,577,846 Field Dec. 11, 1951 2,663,612 Gibson Dec. 22, 1953 2,930, 70 Br d w M 2 60 

1. THE PROCESS OF DYEING AN ALPHA-OLEFIN POLYMERIC MATERIAL HAVING A PARAFFINIC CHAIN AS THE NUCLEUS AND HAVING A SOFTENING POINT 100*C. TO PRODUCE A LIGHTAND LAUNDERING-FAST COLOR SHADE ON SAID MATERIAL, WHICH COMPRISES APPLYING TO THE SURFACE OF THE MATERIAL IN FINELY DISPERED FORM AN ORGANIC DYE HAVING THE PROPERTIES OF BEING HEAT AND LIGHT STABLE AND WITHOUT ASSISTANT AGENT OF BEING INSOLUBLE IN LIQUID PARAFFIN WAX AT A TEMPERATURE UP TO 60*C. BUT SOLUBLE IN SAID PARAFFIN WAX AT LEAST AT A TEMPERATURE SLIGHTLY BELOW THE SOFTENING POINT OF THE POLYMERIC MATERIAL, SAID DYE BEING FORM TO A WATER INSOLUBLE FORM AND IN THE ABSENCE OF ANY VOLATILE SOLVENT FOR SAID DYE AT A TEMPERATURE BELOW THE TEMPERATURE AT WHICH SAID DYE WOULD BE SOLUBLE IN LIQUID PARAFFIN WAX, AND HEATING THE POLYMERIC MATERIAL WITH THE DYE APPLIED THERETO WHILE SAID DYE IS IN DRY FORM TO A TEMPERATURE RANGING BETWEEN THE TEMPERATURE AT WHICH SAID DYE IS SOLUTION IN LIQUID PARAFFIN WAX AND A TEMPERATURE SLIGHTLY BELOW THE SOFTENING POINT OF THE POLYMERIC MATERIAL, TO CAUSE THE DYE IN THE DRY STATE TO BE DIFFUSED INTO AND FIRMLY ABSORBED WITHIN THE INTERIOR OF THE MATERIAL. 